Ella Pallister was a student at Thomas Hardye School in Dorchester.
In a statement the school said: "We are devastated by the news of the tragic and sudden death of Ella Pallister.
"She was studying in Year 13 and she was a popular, bubbly, hard- working and caring student.
"Her closest friends are in shock, but the whole sixth form and school community are grieving for her loss.
"Our thoughts and condolences are with her family at this very sad time."
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A dull and damp start but it will become drier and brighter from the north this afternoon but stay cold and windy.
A damp and cold night ahead. Valentine's Day will start cloudy but become brighter in the afternoon. Risk of showers along the Kent coast.
Cold and damp tonight with outbreaks of rain. A cold and dull start to Valentine's Day but becoming drier and brighter by the afternoon.